<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    .box {
      width: 40%;
    }

    .inner-box {
      background: #908aef;
      padding-bottom: 75%;
      position: relative;
    }
    .content {
      position: absolute;
      inset: 0;
    }
  </style>
</head>
<body>
<div class="box">
  <div class="inner-box">
    <div class="content">
      内容
    </div>
  </div>
</div>
</body>
</html>